A light-emitting diode (LED) is a semiconductor device that converts electric current into light and is mainly used as a light source of a display device. Such an LED exhibits very excellent properties in terms of a small size, low power consumption, a long lifetime, and a fast response time when compared to conventional light sources. In addition, an LED is environment-friendly because it does not release harmful electromagnetic waves such as ultraviolet light and also does not use mercury and other discharge gases. An LED is usually formed by combining an LED light source using a wavelength converting particle such as a phosphor.
Conventionally, a colloidal quantum dot has been used as the wavelength converting particle. A quantum dot generates stronger light at a narrower spectral width than a typical phosphor. Light emission of a quantum dot is achieved when excited electrons transit from the conduction band to the valence band. The same material has a wavelength that varies depending on its size. A quantum dot may emit light of a shorter wavelength as the quantum dot decreases in size. Accordingly, it is possible to obtain light of a desired wavelength region by adjusting the size of the quantum dot.
A quantum dot may emit light even when an excitation wavelength is arbitrarily selected. Accordingly, it is possible to observe light of several different colors at once by exciting several kinds of quantum dots with a single wavelength excitation light. Also, since a light emission in a quantum dot only occurs through the transit from the conduction band minimum to the valence band maximum, a light emission generally has single emission color.
A quantum dot is a nanocrystal of a semiconductor material having a diameter of about 10 nm or less. A vapor deposition method such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) or a chemical wet method in which precursors are inserted into an organic solvent to grow a crystal is used to form the quantum dot. The chemical wet method, which is a method of adjusting crystalline growth with an organic solvent naturally coordinated on a quantum dot determination surface to serve as a dispersing agent when a crystal is grown, has advantages over a vapor deposition method such as MOCVD or MBE because the chemical wet method can adjust uniformity in size and form of a colloidal nanocrystal through an easier and cheaper process.
However, a quantum dot has disadvantages in that the quantum dot is too unstable to be used as a wavelength converting material and has a limited color purity and luminescent effect. Accordingly, developing a wavelength converting material that is more stable and has improved color impurity and light emission performance is urgently required.